1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The disclosed concept also relates to charging assemblies for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit.
Some low and medium voltage circuit breakers, for example, further employ a spring-operated stored energy assembly. Specifically, the operating mechanism of such circuit breakers typically includes an opening assembly having at least one spring, which facilitates the opening (e.g., separation) of the electrical contact assemblies, a closing assembly including a number of springs that close the electrical contact assemblies, and a charging mechanism for charging the spring(s). The contact assemblies are closed by releasing the stored energy of the closing assembly spring(s). The spring(s) is/are charged by a charging assembly which is operated manually, using a manual charging mechanism such as, for example, a charging handle, and/or automatically using a motor-driven charging mechanism or other suitable electromechanical charging mechanism.
FIGS. 1A-1D show one non-limiting example of a circuit breaker 1 (partially shown) having a spring charging assembly 9 for charging a number of closing springs 11 (one is shown in the side elevation view of FIGS. 1A-1D). The spring charging assembly 9 includes a charging cam 13 and a compression arm 15, which cooperates with the charging cam 13 to compress and thereby charge the closing spring 11 (see FIG. 1A). The compression arm 15 pivots (e.g., counterclockwise from the perspective of FIGS. 1A-1D) in response to the contact force applied to it by the closing spring 11. Thus, by virtue of the design (e.g., without limitation, shape) of the compression arm 15 and/or the charging cam 13, the closing spring 11 has the effect of producing a relatively significant amount of torque on the compression arm 15. Consequently, interaction of the compression arm 15 with relatively small changes in the curvature of the charging cam 13 undesirably results in relatively large changes in torque. As such, very close control must be kept of the precise shape of the charging cam 13 to control movement of the spring charging assembly 9 and ultimately, the latch load (e.g., the force applied by the closing spring 11 to the linking assembly 5 of the spring charging assembly 9).
Among other disadvantages, the requirement for such close control of the charge cam geometry increases the cost to manufacture the spring charging assembly 9 and, in particular the charging cam 13 therefor, and decreases the robustness of the overall design because certain components (e.g., without limitation, charging cam 13; compression arm 15) are exposed to considerable force during operation, which undesirably increases wear and tear.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in charging assemblies therefor.